Placing different types of Grass
From what i know there is no such thing as Weight group in Blender.
What you need to do Crissie, is:


Create 3 vertex groups - north(reaching from the edge of the east-west road to the last north most vertex), south (reaching from east-west road edge to the north most vertex), and weed (those two earlier groups combined, so all terrain except the east-west road) and assign appropriate vertices with weight 1 to them.
Use weight paint to cover lake part with weight 0 for south group.
Use the same method to cover road and pavement with weight 0 for north group.
Use the same method to cover road,pavement and lake for weed group
Use north group for Density in Bahia particle system,
Use south group for Density in Rye particle system,
Use weed group for Density in weed particle system.